Structural and chemical stabilization of the epitaxial silicene

The silicon counterpart of graphene, the so called "silicene", has been so far a fascinating theoretical hypothesis, but only recent efforts have pushed it to concrete evidence thus triggering a tremendous interest in silicene for electronic applications and fundamental investigations. Indeed, in addition to graphene, silicene is expected to provide an intimate affinity with the Sibased technology but, unlike graphene, the silicene appears as a buckled lattice where various superstructures take place depending on the periodic distribution of buckled bonds. Here we elucidate the atomistic details of the 4x4 and ?13 × ?13 silicene superstructures epitaxially grown on Ag(111) substrates. These silicene layers have been successfully encapsulated with Al2O3 in order to access ex situ Raman spectroscopy. The Raman spectrum of the encapsulated silicene has been self-consistently interpreted upon comparison with ab initio calculated spectra. In addition to the presence of the double degenerate E2g mode, typical for honeycomb lattices, the non-uniform bond length and the nonsymmetric buckling in the silicene layer introduce an intrinsic disorder which gives rise to disorder activated Raman extra-peaks.